Four men were arrested on Friday afternoon in Pretoria for allegedly possessing and trying to sell an "industrial radiation device," police said.

The four, all South Africans, were caught in Garsfontein in Pretoria East at a petrol station where they had been trying to sell the device, spokesman for the police's elite investigation team, the Hawks, Musa Zondi, said in a statement.

The Hawks, Interpol and other police units took part in the operation.

Zondi said the police received information that people were trying to sell the device for about R45 million.

"A bogus transaction was arranged and the suspects duly arrived and tried to sell off a sample of their consignment."Continues Below ↓

The gadget was secured and taken by the Nuclear Energy Corporation of SA for safe storage. It was not yet clear where it came from. Zondi also did not want to divulge what it could be used for.

"Where it comes from is part of the ongoing investigation. What it can do? It is an industrial device, but some people could do other things with it."

The four would appear in court soon on charges of theft and possession of a radioactive device, as well as charges relating to violating health legislation for handling such material in public.